Dry cleaning method



United States Patent f 3,505,005 DRY CLEANING METHOD Herman SpencerGilbert, Angleton, Tex., assignor to The Dow Chemical Company, Midland,Mich., a corporation of Delaware No Drawing. Filed Feb. 8, 1965, Ser.No. 431,206 Int. Cl. D061 1/04; Clld 7/50 US. Cl. 8-142 Claims ABSTRACTOF THE DISCLOSURE The present invention concerns the method ofcontacting a dry cleaning solvent formulation after use to the action ofa cation exchange resin or a chelating agent to remove or chemicallybind the metal ions in said solvent formulation in a form such that theyare removed from the solvent formulation before the formulation isreused.

It has now been discovered that the presence of polyvalent metal cationsin dry cleaning solvent systems is detrimental to the effectiveness andefficiency of dry cleaning operations. This surprising and unexpecteddiscovery resulted from observations that the reflectance readings ofcloth samples were influenced by the polyvalent metal ion content of thedry cleaning solvent system in which the samples had been cleaned.

In general dry cleaning practice a solvent system comprising essentiallyan organic dry cleaning solvent is employed, e.g. chlorinatedhydrocarbons such as perchloroethylene, trichloroethylene and the like,or volatile hydrocarbons such as benzene, naphtha and the like, and isfrequently formulated to contain detergents or soaps and otheradditives. The term solvent system is used herein to designate thesecomonly used solvents and formulated solvents.

In the present invention the polyvalent metal ion content of the drycleaning solvent system is reduced by contacting the solvent system witha material capable of tying up or precipitating polyvalent metal ions ina form suitable for removal from the solvent system by filtration.Examples of materials found suitable for establishing the ions in a formfor removal, as for example by filtration, include cation exchangeresins, which tie up polyvalent metal ions through ion exchange, andcompounds or compositions which react with polyvalent metal ions to formprecipitates in the solvent system.

Although the concentration of polyvalent metal ions in dry cleaningsolvents may be quite low initially, there is a rapid build-up of thesemetal ions, together with other impurities, during repeated cleaningoperations which remove these impurities from the fibrous materialscleaned. In usual practice, the dry cleaning solvent is continually orperiodically filtered in order to remove the various suspended ordispersed impurities, such as soil particles and the like, whichaccumulate in the solvent during cleaning operations. The interferingpolyvalent ions are not removed by this filtration. However, in practiceof the method of the present invention the undesirable metal ions areestablished in a form removable by such a filtration step. Similarly,the desired removal of polyvalent metal ions, which have beenprecipitated from the solvent system, is accomplished by separatefiltration of the solvent system prior to re-use in further cleaningoperations. In an alternative method of the present inventionthecontaminated dry cleaning solvet system is brought into intimatecontact with a cation exchange resin to effect ion exchange removal ofthe polyvalent metal ions.

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The following examples illustrate the detrimental effect on thebrightness of materials caused by deposition of polyvalent metal ionsonto the material. The tendency of polyvalent metal ions to deposit onmaterials from title cojntacting dry cleaning solvent system is alsodemons rate EXAMPLE 1 After the discovery that polyvalent metal ionstend to be deposited from dry cleaning solvent systems onto materialscleaned therein and that such deposits adversely alfect the brightnessof the cleaned materials, experiments were conducted to determinequantitative effects of this unexpected phenomenon. Investigationrevealed that the polyvalent metal ion deposit is, in most nstances,especially marked where moisture is present in the material. Moisture,of course, is normally present in materials being cleaned and additionalmoisture is generally present in the formulated dry cleaning solventinitially introduced into the dry cleaning system.

A series of forty loads of clothes, averaging about elght pounds perload, were cleaned in a regular commercial dry cleaning machineemploying a standard perchloroethylene dry cleaning solvent system usedin the cleaning industry. A number of new, 4" by 11" swatches of cotton,wool, viscose taffeta and spun acetate materials were cleaned togetherwith this series of 40 loads of clothes and the deposit of polyvalentmetal ions thereon was determined by emission spectroscopy. A portion ofeach of the swatches was moistened with a few drops of deionized waterprior to each cleaning cycle to demonstrate the effect of moisture,present in the material being cleaned, on the tendency of the metal ionsto deposit on the cloth. The original metal content of these newswatches provides a standard for determination of the amounts of metaldeposited during cleaning. The results are shown in Table I, below,where metal content is reported as parts per million (ppm), weight ofcloth basis.

TABLE I Metal Content (p.p.m.)

Swatch and Description Ca Mg Fe Cu Ti Zn Pb Cd Cotton:

New 47 15 14 1 5 2O 10 23 27 25 35 10 65 30 24 Dry area 160 21 22 33 1342 30 20 47 15 340 65 Spun acetate:

New 48 2 1 20 10 2 Wet area..- 150 34 2 1 20 10 16 Dry area 230 70 30 120 1O 10 The largest increase in metal content was at the wetdryinterface and this area also showed the greatest loss of reflectance ascompared with the new sample. This may possibly explain the difficultyencountered in removing the border line portion of water spots; afrequent problem in dry cleaning of materials. This high metal contentat the wet-dry interface is believed due primarily to wet areadeposition with subsequent capillary action (similar to paper partitionchromatography) depositing a large portion of the wet area metal speciesin the ring forming the wet-dry interface.

EXAMPLE 2 This experiment illustrates the correlation betweenreflectance loss and the presence of polyvalent metals in a dry cleaningsolvent system used to clean swatches of material.

A series of cloth swatches was agitated for extended time periods inquantities of three different commercially available dry cleaningsolvent systems. In each case the reflectance readings of swatchesagitated in samples of the new, uncontaminated dry cleaning solventsystem were compared with reflectance readings of swatches agitated inportions of the same dry cleaning solvent system which had beensaturated with Zn, Cu, Fe, and Mg ions. These saturated portions wereprepared by extended stirring of water soluble salts of these metalspecies with the dry cleaning solvent employed. The reflectancereadings, taken on a standard reflectometer, are tabulaed in Table II,below, as taken initiall and at the end of one, two and three days ofagitation in the solvent. In the following table, Solvent 1 isperchloroethylene; Solvent 2 is a chlorinated hydrocarbon dry cleaningsolvent, containing a petroleum sulfonate base detergent, widely used incommercial, coin-operated, dry cleaning machines; Solvent 3 is aformulated perchloroethylene solvent containing a phosphate basedetergent additive.

TABLE II.REFLECTANCE READINGS 1 day 2 day 3 day Spun acetate swatches: 1

Solvent 1:

Metals absent 84. 5 84. 5 84. 5 Metals present 84. 82.5 81. Solvent 2:

Metals absent 84. 5 84. 0 84. 0 Metals present 83. 0 80. 5 78. 5 Solvent3:

Metals absent- 83. 5 83. 0 83. 0 Metals present 82. 0 78. 5 78. 5Worsted gabardine wool swatches: 2

Solvent 1:

Metals absent 73. 0 73. 0 73. 0 Metals present 70.0 68. 0 67. 5 Solvent2:

Metals absent 73. 0 72. 5 73. 0 Metals present 71. 5 67. 5 65. 0 Solvent3:

Metals absent 72. 5 72. 5 72. 5 Metals present 71. 0 69. 5 69. 5

1 Initial reflectance reading-85 units. 1 Initial reflectancereading-73.5.

As shown by the comparative reflectance readings in Table II, above, thepresence of the polyvalent metal ions (which were the only contaminantspresent in the test samples of solvent) cause a significant loss ofwhiteness in the swatches.

As previously noted, one procedure for reducing the polyvalent metal ioncontent of the solvent system involves contacting the solvent systemwith compounds or compositions which react with these metal ions to formprecipitates which are removed from the solvent system as, for example,by filtration. The compounds or compositions employed for this purposeare those which possess the property of forming chelates or complexeswith polyvalent metal ions. Any of the wide variety of known polyvalentmetal ion chelating compounds may be employed for this purpose, such as,for example, the tetrasodium salt of ethylenediaminetetraacetic acid,the pentasodium salt of diethylenetriamine pentaacetic acid, thetrisodium salt of N-hydroxyethylenediaminetriacetic acid and the sodiumsalt of N,N-di(2-hydroxyethyl)glycine. Since these well known chelatingagents are insoluble in the dry cleaning solvent system, except for verysmall amounts which would tend to dissolve in moisture present, it isnecessary that only suflicient agitation or mixing of the insolublecompound and solvent system occur to bring the compound into reactivecontact with the polyvalent metal ions present.

In another procedure, polymers of cyclic amides, such aspolyvinylpyrrolidone, polyvinylmorpholinone, oly-5-methyl-3-vinyl-2-oxazolidinone and mixtures thereof, are added to thesolvent system, with agitation, to form polyvalent metal ion-polymercomplexes which are insoluble in the solvent system and which formprecipitates removable by filtration.

In an alternative procedure the solvent system may be agitated with acation exchange resin, or passed through an ion exchange column of sucha resin to reduce the polyvalent metal ion concentration by ionexchange.

The following examples describe completely representative specificembodiments of procedures for accomplishing the method of the presentinvention, i.e. reducing polyvalent metal ion content in a dry cleaningsolvent system. These examples, however, are not to be interpreted aslimiting the invention other than as defined in the claims.

EXAMPLE 3 In this experiment various compounds and compositions withinthe scope of the invention were employed as additives to a dirty, i.e.mature, solvent system. A quantity of 11.4 grams of the additive wasadded to a 12 liter sample of mature dry cleaning solvent system whichhad previously been used to dry clean clothing. In each case, a quantityof 21 grams of diatomaceous earth was also introduced to serve as afilter medium. After thorough mixing of the mature solvent system andadditive, the mixture was filtered and the residue remaining fromevaporation of a ml. portion of the filtrate was analyzed for metalcontent by emission spectroscopy. Table III, below, indicates theadditive employed and the metal content analysis. The control sample runwas identical to the test sample runs with the exception that no aPolymer of 5-methyl-3-vinyl-2 oxazolidinone. b 50-50 mixture (by weight)of polyvinylpyrrolidone and polyvinylmorphollnone.

EXAMPLE 4 A 55 ml. quantity of a mature solvent obtained from acommercial dry cleaning establishment was agitated for 16 hours with 10grams of a sulfonated styrene-divinylbenzene cation exchange resin (H+form) sold under the trademark Dowex 50 resin (a product of The DowChemical Company, Midland, Mich.). The liquid phase was filtered oil andanalyzed for metals by emission spectroscopy. Table IV, below, shows thepercent of various metal ions removed by this treatment based on theamounts of metal ions originally present. Original metal ion content wasdetermined by an analysis of a control sample before treatment with theion exchange resin.

TABLE IV Percent removal of metal ions organic dry cleaning solventsystem in which an organic dry cleaning solvent is contacted with saidtextile, removed from said textile and the solvent reused, theimprovement which consists essentially of the step of reducing thepolyvalent metal ion content of the solvent system by contacting thesolvent before reuse as a cleaning agent with a sulfonatedstyrene-divinyl benzene acid form of a cation exchange resin which isinsoluble in said system, said resin being employed in an amount fromabout 180 grams to about 0.95 gram per liter of solvent to remove atleast some of the dissolved metal ions from the solvent, while incontact with said solvent, and returning the so treated solvent forreuse in said dry cleaning system.

2. In the method of cleaning fibrous materials in an organic drycleaning solvent system in which an organic dry cleaning solvent iscontacted with said textile, removed from said textile and the solventreused, the improvement of reducing the polyvalent metal ion content ofthe solvent system by treatment of said solvent before reuse with anorganic chelating agent to form an insoluble complex with saidpolyvalent metal ions dissolved in said solvent and removing byfiltration the so-formed complex from the solvent system, said agentbeing employed in an amount from about 180 grams to about 0.95 gram perliter of solvent to remove at least a part of said dissolved metal ions,and returning the so treated solvent for reuse in said dry cleaningsystem.

3. In the method of dry cleaning fibrous materials in a dry cleaningsolvent system which comprises the successive steps of introducing thefibrous material into the solvent system, circulating the solventthrough the fibrous material and filtering the solvent for subsequentre-use in cleaning additional fibrous materials, the improvement whichcomprises the step of reducing the polyvalent metal ion content of saidsolvent system prior to said re-use by contacting the solvent beforereuse and filtering with either a sulfonated styrene divinyl benzeneacid form cation exchange resin or an organic metal chelating agent inan amount from about 180 grams to about 0.95 gram per liter of solventto remove at least a part of the dissolved metal ions from the solventprior to reuse by exchange from solution with said cation exchange resinor the formation of a solid complex with said chelating agent.

4. In the method of cleaning textile materials in an organic drycleaning solvent system in which an organic dry cleaning solvent iscontacted With said textile, removed from said textile and the solventreused, the improvement which consists essentially of the step ofreducing the polyvalent metal ion content of the solvent system bycontacting the solvent before reuse as a cleaning agent with a cationexchange resin which is insoluble in said system, in an amount fromabout grams to about 0.95 gram per liter of solvent to remove at leastsome of the dissolved metal ions from the solvent, and returning the sotreated solvent for reuse in said dry cleaning system, which cationexchange resin is a sulfonated styrene-divinyl benzene cation exchangeresin hydrogen ion form.

5. In the method of cleaning fibrous materials in an organic drycleaning solvent system in which an organic dry cleaning solvent iscontacted with said textile, removed from said textile and the solventreused, the improvement of reducing the polyvalent metal ion content ofthe solvent system by treatment of said solvent system with an organicmetal chelating agent to form a solid complex with said polyvalent metalions and removing the so-formed solid complex from the solvent systemand returning the so treated solvent for reuse in said dry cleaningsystem, said chelating agents are employed in amounts of from about 180grams to about 0.95 gram per liter of solvent and are selected from thegroup consisting of tetrasodium salt of ethylenediamine tetraaceticacid, trisodium salt of N-hydroxyethylenediaminetriacetic acid, sodiumsalt of N,N-di(2-hydroxyethyl)glycine, and the polyvinylpyrrolidone,polyvinylmorpholinone, poly- 5-methyl-3-vinyl-2-oxazolidinone, andmixtures of the polymers.

References Cited UNITED STATES PATENTS 3,057,676 10/1962 Wedell et al.

3,238,011 3/1966 Lawrence et al. 252153 3,173,862 3/1965 Clements et al210-138 2,723,222 11/1955 Stark 252-89 2,874,124 2/1959 Vitalis 252-893,000,830 9/1961 Pong et al 252-89 3,317,424 5/ 1967 Schmidt 210 24OTHER REFERENCES .RoseThe Condensed Chem. Dictionary (6) 1961, ReinholdPubl. 00., p. 1013.

LEON D. ROSDOL, Primary Examiner W. SCHULZ, Assistant Examiner US. Cl.X.R.

